Typically, multiphase parallel DC/DC converters are used to implement the power supplies for devices that require low-voltage and high-current supply, such as central processing units (CPUs). Especially, for devices subject to stricter specifications, the power supplies are further required to provide active voltage positioning (AVP) function. In low-voltage and high-current applications, multiphase parallel DC/DC converters can increase heavy-load conversion efficiency, while they are disadvantageous with poor efficiency at light-load. For multiphase parallel DC/DC converters to have high conversion efficiency at both light-load and heavy-load, dynamic phase control is proposed. For example, U.S. Pat. No. 6,674,274 detects the output current value by monitoring the output voltage variation caused by AVP. According to the AVP principle, the output voltage decreases responsive to an increased output current, and the converter system is switched to multiphase operation for increasing the heavy-load conversion efficiency; on the contrary, the output voltage increases responsive to a decreased output current, and the converter system is switched to single-phase operation for increasing the light-load conversion efficiency. Alternatively, U.S. Pat. No. 7,492,134 detects the output current value by monitoring the phase currents of the converter system for determining the number of active phases. When the phase current increases, the number of active phases gradually increases, and when the phase current decreases, the number of active phases gradually decreases. Additionally, when detecting instant drop of the output voltage, the converter system immediately enables all of the phases to accelerate phase change and in turn prevent undesired over-current protection or system damage.
A phase current may suddenly increase due to, for example, an increased output current, a reduced DC load line, or a highly sloped output voltage variation, etc, where the DC load line refers to the voltage drop caused by AVP. All conventional solutions are to change the number of active phases according to the output current value, and thus the speed of changing the number of active phases depends on the speed of current sensing. When the speed of current sensing in the converter system is too high, shift of the output current level and misoperation tends to happen. On the contrary, when the speed of current sensing in the converter system is too low, unnecessary over-current protection or damage may happen. Referring to FIG. 1, the changing slope of a phase current may be divided into three areas A1, A2 and A3, in which the phase current changes fastest in the area A1, slower in the area A2 and slowest in the area A3. The existing methods can only instantly deal with conditions of the phase current with a changing slope in the area A1 or A3 to determine an appropriate number of active phases, and thus, during single-phase operation of the converter system in steady, if the phase current suddenly increases with a changing slope in the area A2, the converter system will not timely switch from the single-phase operation to multiphase operation, which may cause unnecessary over-current protection or system damage.
Therefore, it is desired an enhanced phase control circuit and method to deal with conditions of the phase current with a medium changing speed.